158 Prof. E. J. Chapman on a new Species of Agelacrinites. 



interradial spaces and the margin of the disk are covered by 

 numerous irregularly disposed, scale-like and partially imbri- 

 cating plates. At the margin these are very small, exceedingly 

 numerous, and arranged in three or four irregular rows, with 

 their longest diameter pointing towards the centre of the disk. To 

 these succeed a series of larger plates, having their greatest 

 diameter in a direction at right angles to that of the border 

 plates, or, in other words, parallel with the circumference of the 

 disk. To these succeed, again, other and somewhat smaller 

 plates, all partially overlapping. This arrangement of the surface 

 plates seems to be an extreme modification of that which obtains 

 in A. Hamiltonensis of Vanuxem, and A. Bohemicus of F. 

 Roemer ; but the larger plates merge gradually, as it were, into 

 the others, and thus there is no defined circle of large plates 

 separating (as in the latter types) the border plates from those of 

 the centre. Finally, in one of the interradial spaces, at a 

 distance of about one-sixth of an inch from the centre of the disk, 

 a well-marked "pyramidal orifice" is situated. This, in the 

 specimen under examination, is about one-twentyfourth of an 

 inch in diameter, and is made up, apparently, of ten plates, in 

 two sets of five — one set alternating within the other, as in 

 Hair's Hemicystites parasitica. The under side of our species 

 remains unknown ; but, in the specimen examined, it is not 

 attached to a shell or other organic body, and hence, as shown 

 moreover by examples of other species, the genus cannot pro- 

 perly be considered a parasitic one. 



Agelacrinites Billingsii differs essentially from the Canadian A. 

 Dicksoni of Billings (and also from the Edrioaster Bigsbyi of 

 that palaeontologist) by the possession of short and straight rays, 

 and by its numerous marginal plates. It is also at once distin- 

 guished by its straight rays, independently of other characters, 

 from the typical Devonian species, A. Hamiltonensis of Vanuxem, 

 and the more recently discovered Carboniferous species, A. 

 Kaskaskiensis of Hall. It agrees, on the other hand, somewhat 

 closely with Hair's Hemicystites parasitica^ Agelacrinites para- 

 siticus from the Niagara Limestone of New York ; but in this 

 latter species the rays are very narrow at their orgin, and are 

 connected there (in the centre of the disk) by a small tubercle or 

 rounded plate. In place of becoming narrower also towards the 

 margin (as in A, Billingsii) and terminating in well-defined 

 points, they become rapidly broader, " coalesce with the plates 

 of the body" (Professor Hall), and are altogether undefined at 

 their extremities. These characters, as given in the ' Palaeontology 

 of New York' (vol. ii. p. 245, and plate 51. figs. 18-20), from 

 an examination of several specimens, are exactly the reverse of 

 those which obtain in our new species. Whilst, also (although 



